JPH02238436A - Liquid crystal electrooptical element - Google Patents

Abstract

PURPOSE:To simplify the process for producing the liquid crystal electrooptical element and to reduce the thickness and weight of the element by forming the transparent substrates of a liquid crystal cell so as to serve commonly as optically anisotropic substrate. CONSTITUTION:A homogeneously oriented liquid crystal 9 is crimped between two sheets of the transparent substrates facing each other and at least one of a pair of the substrates 5, 7 is formed as the optically anisotropic substance. The optically anisotropic substance is so formed that certain one refractive index N3e among the three major refractive indices N1o, N2o,, N3e possessed by the substance is smaller than the other two refractive indices N1o, N2o and the axis corresponding to the refractive index N3e exists in the direction nearly horizontal with the substrate surfaces 5, 7. The process for producing the liquid crystal electrooptical element is simplified in this way and further, the thickness and weight of the element are reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a liquid crystal electro-optical device. [Prior Art] In the conventional homogeneous ECB mode, display was performed by controlling the birefringence of the liquid crystal, so the display was heavily colored and the viewing angle was narrow. In order to solve this problem,
In addition to the liquid crystal cell that performs display, it is proposed in Japanese Patent Application No. 63-198 to provide an optically anisotropic body having optically negative uniaxiality.
Proposed in No. 506. Figure 5 shows a cross-sectional view of a conventional liquid crystal electro-optical element. In the figure, 1 is an upper polarizing plate, 2 is a liquid crystal cell, 3 is an optically anisotropic body, and 4 is a lower polarizing plate. The liquid crystal used in the liquid crystal cell was SS-5003 (Δn=0.080) manufactured by Chisso Corporation, and was homogeneously aligned between two transparent electrode substrates.
The liquid crystal layer thickness d was set to 6.0 μm, and the retardation Δ
nd was set to 0.48 μm. On the other hand, for optically anisotropic materials,
A uniaxially stretched polymer film containing polymethyl methacrylate (PMMA) as the main component was used.
Ordinary polymer films have the property that their refractive index increases in the stretching direction when they are stretched, but PMMA, polystyrene, and the like have the property that their refractive index decreases in the stretching direction. The refractive index of this film is the refractive index in the stretching direction N3e=
1.4974, refractive index N2o in the direction perpendicular to this within the film plane = 1. 4978, the refractive index N1o in the thickness direction of the film is 1.4977, and it has optically negative uniaxiality. The film thickness is also set so that the retardation value is approximately equal to or slightly smaller than that of the liquid crystal cell. Here, the film thickness is 1100 μm,
The retardation was set to 0.44 μm. Figure 2 shows the relationship between each axis of a conventional liquid crystal electro-optical element. The angle 21 between the polarization axis (absorption axis) direction 11 of the upper polarizing plate and the rubbing direction 12 of the upper substrate of the liquid crystal cell is 4 to the left.
5@, the angle 22 formed by the rubbing direction 13 of the lower substrate of the liquid crystal cell and the stretching direction 14 of the uniaxially stretched film is 08, the angle 2 formed by the polarization axis (absorption axis) direction 15 of the lower polarizing plate with 14
3 is set to 45' to the right. A conventional liquid crystal electro-optical element manufactured under the above conditions exhibits electro-optical characteristics with extremely little coloration, as shown in Figure 3, when measured from a direction perpendicular to the panel surface. Furthermore, as shown in Figure 4, the viewing angle characteristics are also very good. [Problems to be Solved by the Invention] However, conventional liquid crystal electro-optical elements require a lamination process for the number of uniaxially stretched films than ordinary twisted nematic type (hereinafter referred to as TN type) liquid crystal electro-optical elements. There was an issue of increasing numbers. Furthermore, a stretched film with optically negative uniaxiality has a small absolute value of birefringence and has poor film uniformity, so it tends to be thicker than a normal stretched film. In the case of small portable panels, this increase in thickness and weight was also a major issue. The present invention is intended to solve these problems, and its purpose is to simplify the manufacturing process of a liquid crystal electro-optic device and to make the device thinner and lighter. [Means for Solving the Problems] A liquid crystal electro-optical element of the present invention is a liquid crystal electro-optical element in which a homogeneously aligned liquid crystal is sandwiched between two opposing transparent substrates, in which at least one of the pair of transparent substrates is is an optical anisotropic body, and the optical anisotropic body has 3
Among the two main refractive indexes N1o, N2o%N3e, one refractive index N3e is the other two refractive indexes N1o,
It is characterized in that the axis thereof, which is smaller than N2o and corresponds to its refractive index N3e, is in a direction substantially horizontal to the substrate surface. Further, the optically anisotropic body is a stretched polymer. The details of the present invention will be shown below with reference to Examples. [Example] FIG. 1 shows a cross-sectional view of a liquid crystal electro-optical element in an example of the present invention. In the figure, 1 is an upper polarizing plate, 2 is a liquid crystal cell,
4 is the lower polarizing plate. The liquid crystal used in the liquid crystal cell was 33-5003 (Δn=0.080) manufactured by Chisso Corporation, and was homogeneously aligned between two transparent electrode substrates. The liquid crystal layer thickness was set to 6.0 μm, and the retardation was set to 0.
It was set to 48 μm. The upper substrate 5 and lower substrate 7 of the liquid crystal cell are both plastic substrates. Polyether sulfone (PES) without optical anisotropy was used for the upper substrate.

On the other hand, for the lower substrate, a film made of a polymer mainly composed of PMMA stretched in a uniaxial direction was used. The refractive index of this -axially stretched film is N1o=1.4977, N2o=1.4
978, N3e=1. 4 9 7 3. Since the film thickness is 1100 μm, the retardation is 0.
It becomes 44μm. In addition, the glass transition temperature Tg of these plastic substrates is approximately 150°C in the case of PES,
In the case of PMMA, it is approximately 12010°, so all processes such as sputtering of the transparent electrode and baking of the alignment film are performed at 100°.
I went below C. Figure 2 shows a diagram of the relationship between each axis. The angle 21 between the polarization axis (absorption axis) direction 11 of the upper polarizing plate and the rubbing direction 12 of the upper substrate of the liquid crystal cell is 45 degrees to the left between the rubbing direction 13 of the lower substrate of the liquid crystal cell and the stretching direction 14 of the uniaxially stretched film. Angle 22 is 06 Polarization axis (absorption axis) direction of lower polarizing plate 1
The angle 23 that 5 makes with 14 is set to 45° to the right. As shown in FIGS. 3 and 4, the liquid crystal electro-optical device of the present invention exhibits excellent characteristics similar to those of conventional liquid crystal electro-optic devices. In the above implementation, only one of the pair of plastic substrates was made optically anisotropic, but it is also possible to improve the electro-optic characteristics by making both substrates optically anisotropic. be. Furthermore, the liquid crystal electro-optical element of the present invention includes:
Since the voltage-transmittance characteristic has a better steepness than the conventionally widely used TN method, it can be driven at a duty ratio larger than conventional methods, such as 1/16 to 1/32. Such medium-capacity display elements are ideal for portable information devices, and the present invention has the great advantage of being thinner and lighter. [Effects of the Invention] As described above, according to the present invention, the transparent substrate of the liquid crystal cell also serves as an optically anisotropic body, thereby simplifying the manufacturing process of the liquid crystal electro-optical element, and making the element thinner. It becomes possible to make it a light meal.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal electro-optical device according to the present invention. FIG. 2 is a diagram showing the relationship between the axes of the present invention and a conventional liquid crystal electro-optical device. FIG. 3 is a diagram showing the electro-optical characteristics of the present invention and a conventional liquid crystal electro-optical element. FIG. 4 is a diagram showing the viewing angle characteristics of the present invention and a conventional liquid crystal electro-optical element. FIG. 5 is a cross-sectional view of a conventional liquid crystal electro-optical element. 1. Upper polarizing plate 2. Liquid crystal cell 3. Optically anisotropic body (uniaxially stretched film) 4, lower polarizing plate 5. Upper substrate 6. Lower board 7. Lower substrate (uniaxially stretched film) that also serves as an optically anisotropic body 8. Transparent electrode9. Homogeneously aligned liquid crystal 11. Direction of the polarization axis (absorption axis) of the upper polarizing plate 1 12. Rubbing direction 13 of upper substrate 5 of liquid crystal cell. Rubbing direction 14 of the lower substrate 6 or 7 of the liquid crystal cell Stretching direction 15 of the uniaxially stretched film 3 or 7
．． Direction of the polarization axis (absorption axis) of the lower polarizing plate 4 21. An angle between the direction 11 of the polarization axis of the upper polarizing plate and the rubbing direction 12 of the upper substrate of the liquid crystal cell. 22. An angle between the rubbing direction 13 of the lower substrate of the liquid crystal cell and the stretching direction 14 of the uniaxially stretched film. 23. An angle between the direction 15 of the polarization axis of the lower polarizing plate and the stretching direction 14 of the Go-axis stretched film. 31. fi length 450 nm (7) Light (blue light) vs. voltage transmittance curve. 32. Voltage transmittance curve for light with a wavelength of 550 nm (green light). 33. Voltage transmittance curve for light with a wavelength of 650 nm (red light). 41. Equal contrast curve 42 with contrast ratio 1,
Equal contrast curve 43 with contrast ratio 3. Equal contrast curve 44 with a contrast ratio of 10. Equal contrast curve 45 with contrast ratio 30. Contrast ratio 100 equal contrast 6 to curve or more Applicant Seiko Epson Co., Ltd. agent - Patent attorney Kisaburo Suzuki (and 1 other person) Applied voltage (V) Figure 3, Figure 2

Claims (2)

[Claims] (1) In a liquid crystal electro-optical element in which a homogeneously aligned liquid crystal is sandwiched between two opposing transparent substrates, at least one of the pair of transparent substrates is an optically anisotropic body, and the optically anisotropic body is an optically anisotropic body. has three main refractive indices N1o
, N2o, and N3e, one refractive index N3e is smaller than the other two refractive indexes N1o and N2o, and the axis corresponding to the refractive index N3e is in a direction substantially horizontal to the substrate surface. A liquid crystal electro-optical device featuring: (2) The liquid crystal electro-optical element according to claim 1, wherein the optically anisotropic body is a stretched polymer.